Burner control system



Sept. 2, 1941. V. R. TATE BURNER CONTROL SYSTEM Filed Oct. 24, 1938Patented Sept. 2, 1941 2,254,984 I BURNER comor. SYSTEM Virgil RobinsTate. Milwaukee, Wis., assignor to Perfex Corporation, Milwaukee, Wis.,a corporation of Wisconsin Application October 24, 1938, Serial No.236,656

, 29 Claims.

This invention relates in general to control systems and moreparticularly to oil burner control systems.

In oil burner control systems it is customary to provide some meanswhich will, in case of ignition' failure or flame failure, shut theoil-bumer ,down until such means has been manually reset.

Such means is generally referred to as a safety switch, and usuallyconsists of a switch, a bimetal actuator, and an electric heater; If theelectric heater is permitted to remain energized for too long a period,the actuator opens the switch and it therefore remains open untilmanually reset. Such a safety switch is often referred to as a lockoutswitch. Usually the safety switch heater is energized upon starting theoil burner, and then after combustion has been established the heater isdeenergized, by either opening the heater circuit or shunting it byproviding a short circuit around the heater. The means for deenergizingthe safety switch heater is usually responsive to combustion conditions.Such means is generally referred to as a combustion responsive switch orstack switch. The line voltage circuit for the oil burner motor isusually controlled by means of a relay having its coil in either anotherline voltage circuit, or in a low voltage circuit. The safety switchheater is usually connected'in series with the motor, or in series withthe relay coil, in order that the oil burner cannot operate withoutenergizing the safety switch heater. This necessitates matching theheater to the load when a relay is not used, and additionally usuallyresults a in a bulky heater because of the relatively large startingcurrents. Two such burner control circuits are shown in the copendingapplication of Justin A. Deubel, Serial No. 236,819, filed Oct. 24,1938; and the present invention constitutes an improvement upon theburner control circuits of said copending application. It is an objectof this invention, therefore, to overcome the foregoing objectionalfeatures and provide a control apparatus which has universalapplication.

The primary object of this invention is to provide new and improvedcontrol systems for controlling the operation of automatic fuel burnersand more particularly oil burners.

Another object of this invention is to provide a new and improved safetyswitch arrangement give safe operation without having to connect thesafety switch heater in series with either the motor or any circuitcontrolling the motor.

Another object of this invention is to provide an automatic means forchecking the stack switch operation which will totally deenergize thesystem if the stack switch does not function properly.

Other objects and advantages reside in certain novel features ofconstruction, circuit arrangement, and operation of the variousparts andelements which will be hereinafter more fully described in thespecification, and particularly pointed out in the appended claims, andof which a preferred embodiment is illustrated in the ac .companyingsheet of drawings forming a part thereof, and in Which;

Fig. 1 shows a front elevation of the safety switch and stack switch;

Fig. 2 is a cross sectional view of the stack elements taken along theline 22 of Fig. 1;

Fig. 3 is a left side view of the latch mechanism of the lockout devicetaken along the line 3-3 'of Fig. 1;

Fig. 4 is a right side view'of the latch mechanism taken along the line44 of Fig. 1;

Fig. 5 is a top view of the latch mechanism in its normal engagedposition taken along the line 5-5 of Fig. 1;

Fig. 6 is a fragmentary portion of the lockout mechanism showing theswitch latch released in one direction;

Fig. '7 is a fragmentary portion of the lockout mechanism showing theswitch latch released in the opposite direction;

Fig, 8 is a schematic circuit diagram of one .form of the improvedcontrol system utilizing a -ferred alternative methods of operating the7 safety switch from the stack switch.

which will avoid the necessity of deenergizing Another object of thisinvention is to provide an improved oil burner control circuit whichwill The drawing discloses a preferred embodiment of the invention forthe purpose of explaining and describing the invention. ,In the specificform shown in Fig. 1, afianged metal base 10 is provided, having a panelof insulating material [2 fastened thereto by screws as shown, forsupporting the various elements and parts of the control mechanism. Acombustion responsive means is provided such as a thermal device havinga plurality of elements. One of said elements comprises a relativelyhigh expansive channel member l4 formed into a U-shape, and

a secondelement I6. comprising a relatively low expansive tubular memberrigidly fastened by the rivet I8 at one of its ends to the channelmember I l at the bend of the U. The other end of the low expansiveelement It is slotted and flattened, and is arranged to protrude throughan opening I9 in a support plate 22 and an additional opening 20 in thebase I0. The open ends of the U-shaped channel member It are suitablyfastened to the support plate 22 by rivets 23 as shown. A slip frictionmeans which includes a connector link shown in the drawing as a springblade 24 made of hard, smooth, corrosion resisting material such asstainless steel, is secured to the protruding end of the low expansiveelement It by means of a rivet 26. staked to the support plate 22 at oneend as shown, is a support tube 28. The support plate 22 is fastenedrigidly to the base I by means of screws 30. Hinge supports 32, castintegral with the support plate 22, protrude through the base I0 toreceive a hinge means shown in the drawing as U-shaped steel springhinge 35. The open ends of the U of the spring hinge 33 are clampedbetween a hinge clamp 36 and the hinge supports 32 by screws 38 whichpass thru the two former members and thread into the latter. The baseportion of the U-shaped spring hinge 34 is clamped between a movable.nember such as an actuating arm 33 and a friction block bracket orclamping plate 12 by means of rivets M. The slip friction means alsoincludes two additional elements. One of these elements comprisesa block35 made of friction material such as carbon which is inserted in-acavity or recess in the friction block bracket Q2. The other of theseelements comprises a second block 48 made of friction material such ascarbon, which is inserted in a cavity or recess formed in a frictionblock support member 50, said support being free to move along a pair ofguide pins 52 fastened to the actuating arm 40. The spring blade 2 isclamped between the friction blocks 45 and 48 close to the springhinge34, to form the short arm of 2. ever system so that the relative motionof the hermal elements I4 and It will be amplified at he end of theactuating arm 40. The clamping :fiort upon the friction blocks isapplied by an idjustable means such as a screw 54 threaded .hrough theactuating arm 40, through a comiression spring 56 which is arranged atsuch an ngle that itshorizontal component of force is lways sufiicientto cause the friction block suport 50 to bear against but oneside of theguide wins 52. One end of the compression spring 53 :xtends into arecess 58 formed in a protruding portion 60 on the friction blocksupport 50, and

. the other end. carries a cup-shaped insert 62 rangement the contactsare operated upon changes in temperature independent of actualtemperature. Further details of the construction and operation of thethermal elements and slip friction mechanism may be had by referring toa copending application of William Christiansen, Serial No'. 236,818 andfiled October 24, 1938.

A description of the safety switch device, a further important mechanismin the control system, will now be given in detail.

A first actuator bracket 91 (see Fig. 3) is fastened rigidly to thepanel I2 at one end by a screw 98. A first thermal actuator I00, shownas a U-shaped piece of bimetal, is fastened on the free end of thebracket 91 by a pair of screws I32 passing thru the bracket and thebimetal into a first heater block I04 which is bent into a U- shape andarranged within the actuator I00. A

first heater I06 is clamped in the U-bend of block IM and serves tomotivate the first actuator I00. The heater block 104 serves tosecurelyhold the heater I06 and to additionally control the rate of movement ofthe first actuator I00. A second actuator bracket I0'I (see Fig.. 4) isfastened rigidly to the panel I2 at one end by a screw I03. A secondactuator I I0 shown as a U-shaped piece of bimetal, arranged incompensative relation to the first bimetal actuator I00, is fastened onthe free end of the bracket I01 by a pair of screws I I2 passing thruthe bracket and the bimetal into a second heater block H4 bent into aU-shape and arranged within the bimetal III). A second heater H6 isclamped within the block H 5 and serves to motivate the second actuatorIIO. This heater block H4 serves to securely hold the heater and toadditionally control the rate of movement of thesecond actuator III].

A latch mechanism having two release positions is arranged to cooperatewith the first and second actuators I00 and H0, and is shown to consistof a plurality of elements. A latch bracket H1 is fastened at one of itsends to the first actuator I00 by rivets H8, and is bent back to passrearwardly through an opening H9 cut in which in turn receives the endof the adjusting screw 54. An insulating plate member 14 is fastened tothe actuating arm 40 by screws I6 and serves to further amplify therelative'motion of the thermal elements I4 and I6. It carries a plate I8which is fastened to it by rivets '80. Two switch actuating screws 02and 84 are threaded into'the plate 18. A switch bracket 86 is fastenedto the panel I2 by screws 88.

. Fastened to-the switch bracket 86 is a pair of.

cold spring contacts 90 operated by the screw 82. Fastened to the panelI2 is a pair of hot spring contacts 92 operated by thescrew 84.. A

- hot stop pin 94 and a cold stop pin 96 are fastened to'the switchbracket 86. After the arm 40 engages the stops '94 and 96 the blade 24slides between the friction blocks 46-48. By this arthe panel I2. Alatch spring I20 is fastened to the free end of the latch bracket II'Iby rivets I22, and is arranged to pass forwardly thru the opening I I9in the panel I2. Adjacent the fastening point of the latch spring I20,one end of a latch member shown as an L-shaped member I24 with a latchI25 is fastened to the latch spring I20 by rivets I26 andextendsiorwardly thru the panel opening H9 along with the latch springI20. A release member shown as an L-shaped member I28 with a trigger I20isfastened to the free end of the second actuator H0 and is arranged tobe perpendicular to andnormally in engagement with the latch I25. The

release member I28 is insulated from the second actuator IIO by aninsulating member I30 which is fastened to the second actuator by rivetsI32, and to the release member by rivets I34. A contact bracket shown asan L-shaped bracket I36 is additionally fastened to the second actuatorby the rivets I32. A latch contact I38 which engages the latch springI20 is fastened to the contact bracket I36.

A reset mechanism is provided to manually reset the latch member I24 toits normal position after'it has been released. This mechanism is shownto comprise a resilient resetting member I40 rigidly fastened to thepanel I2 at one end by the screw 98 and an additional screw I42; 9.sliding bar member I46 passing thru the base for manually operating theresetting member I40 and having a notch I48 cut in it forengaging a.projection I50 formed 'on the resetting member I40; and a combinationstop and switch member I52 fastened to the panel ,I2 against which theresetting member I40 normally rests and com-' pletes circuit connectiontherethru. Projection I50 on the resetting member I40 extends thru anopening I I9 in the panel I2 and also serves to limit the motion of theresetting member I40 under action of the bar I46 by engaging the edge ofthe panel opening I54. Additional projections' I56 and I58 are alsoprovided on the resetting member I40 to respectively loosely hold thesliding bar member I46 in place and to enage the-latch member I24 whenit is reset.

An adjusting screw I60 passing thru the panel I2 and threaded into thefirst actuator bracket 91 serves to adjust the relative position of thefirst actuator I with respect to the second actuator I I0 and henceadjust the setting or calibration of the safety switch by adjusting thelatch I25 with respect to the position of the trigger I29. A secondadjusting screw I62 passing thru the panel I2 and threaded into thesecond actuator bracket I01 serves as an additional adjustment for thelatch I25.

The safety switch is so arranged that a circuit path is provided thru itextending from the wire attached to the stop member I52, thru theresetting member I40, the screw 98 holding the resetting member I40, thefirst actuator bracket 91, first actuator I00, the latch bracket I I1,the latch spring I20, the contact I38, the contact bracket I36, thesecond actuator H0, and finally thru the second actuator bracket I01 toa wire attached thereto. When the safety switch is opened or locked outthe circuit thru it is interrupted at the contact I38 by the latchspring I20.

Now referring particularly to the control system shown in Fig. 8.Alternating current is fed over the line conductors I64 and I66 thru thelimit control and passes thru the circuit of the safety switchpreviously described, to a stepdown transformer I68. A relay I 10 andthe first heater I06 associated with the first actuator I00 areenergized in parallel from the low voltage sec-- ondary of thetransformer I68 by means of the room thermostat. contacts I 12. Therelay contacts I14 control an ignition means I16 and a fuel motor I18wired in parallel therewith, by connecting them to the lines I64 and 166thru the limit control and the safety switch. The second heater II6associated with the second bimetal I I0 is energized directly from thesecondary winding of the transformer I 68 thru the stack switch hotcontacts 92.

Assume now that the control is mounted in the I6. This motion istransmitted to the actuating arm 40 thru the slip friction connection2446--' 46 and causes closure of the hot contacts 92, which effect theenergization of the second heater II6 thru the circuit pointed out. Inresponse end away from the panel I2 closely following the first actuatorI00. Thus the latch I25 and the trigger I29 remain engaged andconsequently the circuit thru the safety switch is maintained. Uponreaching their ultimate positions the two actuators resume approximatelythe same relative positions they had when cold and remain so relatedduring the entire ensuing normal operation of the fuel burning means.When the stack temperature reaches a sufficiently high tempera-- turethe actuating arm engages the hot stop 94. Then upon additional stacktemperature rise the slip friction mechanism is brought into operation.The spring blade 24 slides between the carbon blocks 46 and 48 andallowsthe thermal elements to move independent of the actuating arm.

If combustion is not established, however, as a result of theenergization of the fuel burning means, the second heater H6 is notenergized because the actuating arm 14, under these conditions, is notmotivated and the stack contacts alone and the latch I25 fastened to itslides stack of an oil burning furnace and that all the elements are intheir normal inactive positions. When the room thermostat calls for heatin response to a drop in the room temperature, the relay I10'and theheater I06 are energized over the circuit described. In response to theheat on the trigger I29. After some period of time, depending upon thecalibration or setting of the latch I25 with respect to the trigger I29,the relative motion between the two actuators I00 and H0 becomessufiicient to cause the latch I25 to be released by the trigger I29.Upon being released the latch member I24 is snapped over to the lockoutposition shown in Fig. 6 in response to the biasing action of the latchspring I20. The circuit thru the safety switch is thereby opened atcontact I38, and the fuel burning means is consequently shut down untilthe safety switch is manually reset. The safety switch is usuallycalibrated or set to lockout in a definite predetermined time under thiscondition of operation. Other things being equal, the safety switchtiming under other conditions of operation is hence dependent upon thissetting. The relative safety switch timings under various conditionsofoperation, however, can be modified by changing the physical dimensionsof the engaging portions I25 and I29 of the latch and release membersl24and I28.

Assume now that the control device and the fuel burning means havefunctioned normally in response to the thermostats call for heat andhave reached their normal running positions. When sufficient heat hasbeen generated to satisfy the thermostat, thermostat contacts I12 opendeenergizing the first heater I06 and the relay I10 but not the secondheater H6. The relay I10 opens the relay contacts I14 and shuts down thefuel burning means I16-I18. After a short time combustion ceases and thestack temperature drops effecting an initial relative movement of thethermal elements which in turn initiates movement of the actuating arm40 in the cold direction. When the temperature of the thermal devicedrops a predetermined amount, the hot contacts 92 open and the secondheater H6 is deenergized before suflicient relative motion has occurredbetween the firs to operate perfectly.

and initiate motion of the actuating arm 50 in the cold direction. Afterthe stack temperature drops a predetermined amount the contacts 92 opendeenergizing the second heater H6, and causing the secondactuator I I!)to move toward its cold position. The relative distance between theenergized first actuator and the cooling deenergized second actuatorincreases until finally the trigger I29 releases the latch I25 and thesafety switch opens as shown in Fig. 6. The safety switch-deenergizesthe system upon opening and shuts it down so that it cannot be restarteduntil the safety switch is manually reset.

To reset the safety switch the sliding bar member M6 is pushed inwardtoward the base. This motion is transmitted to the resetting member IdIlby means of the notch I48 on the sliding member Hi6 and the engagingprojecting member I50 on the reset member 0. As the movement of thesliding member progresses the lower end of the resetting member I40moves away from the combination stop and switch member W2, and theprojecting-member I58 engages and moves the latch member I24 against theeffort of the latch spring I20 so that the latch I25 assumes a positionin back of the trigger I29 on the releasing member I28. The separationof the resetting member IEO from its stop I52 disables the burner systemuntil the bar I45 is restored by the tension of member I40. Thisprevents the operation of fuel burning system while thesafety switchelements I20 and I38 are normally held in engagement and hence out-ofcontrol of the actuators I and III].

The foregoing description of the operation of the device has assumed thecontrol mechanism Now assume again thatthe control device and the fuelburning means have functioned normally. in response to the thermostatope'ration and have reached their normal ditions.. Assume contacts I12at this time and combustion ceases.

Under these conditions, when the safety switch operates to lockout theto trip as shown in Fig. '7. The system is thereby rendered inoperativeuntil the secondactuator cools and the safety switch can be manuallyreset. After being manually reset the system will continue to lockoutafter every burner operation until the actuating arm is again made tooperate satisfactorily. From the foregoing explanation it may be seenthat the control system checks the operation of the stack switch in boththe hot and cold directions and shuts down the entire system if thestack switch does not go thru its complete cycle of operation for everycycle of operation of the fuel burning means.

Now assume again that the control device and the fuel burning means havefunctioned normally in response to the operation of the thermostat andhave reached normal running conditions. Now, if either the first or thesecond actuator heaters I06 or MS become deenergized because of a.failure of either of the heaters, or for any other reason, the switchwill lockout as shown in either Figs. 6 or 7 depending upon which of thetwo heaters becamedeenergized. One of the actuators remains energized inits hot position while the other cools. Eventually the relative distancebetween the two exceeds the safety switch setting and the switch trips.If the first actuator heater I06 becomes deenergized, the latch I25 willbe released by dropping off one side of the trigger I29 releasing thelatch member I24 and opening the switch as shown in Fig. 7. If thesecond actuator heater-becomes deenergized, the latch l25 will bereleased by dropping off the other side of the trigger I29 releasing thelatch member I24 and opening the switch as shown in Fig. 6. Also, ifeither the first or second heater I06 or II6'fail or become inoperativeduring the time the system is not in operation,- the safety switch willproceed to a safety lockout on the subsequent operation in response tothe thermostat action. Since the two 1 actuator heaters have separateenergizing circuits, although oneof the heaters fails, the other will beenergized upon normal operation of the burner and will serve to shut thesystem down by looking out the safety switch as shown in either Fig. 6or Fig. 7, depending upon which heater fails to function. The limitcontrol, as is well known, serves to shut down the system if excessivetemperature, pressure, etc.', conditions are reached and to'automatically start up the sys- ,.60 ru nn'ing -c0nthat the thermostatopens its Further assume, because of failure'in the mechanism, theactuating arm 40 fails to move from its hot position; The first actuatorI00, being deenergized by the thermostat, slowlycools toward its coldposition, but the second actuator IIO, being independently energized bythe hot contacts 92, remains in its hot position. After a short lapse oftime the relative distance between the two actuators, due to the motionof the first actuator, exceeds a certain value corresponding to thesafety switch setting, and the trigger I29 releases the latch I25causing the safetyswitch tern again when normal conditions arereestablished.

Fig. 9 showstwo alternative methods of utili 7 ing the control elementsin the system when a low voltage relay is not used. With the mechanismshown in solid lines, the control operates in identically the samemanner as described for Fig.

8 except that in this case thethermostat controls the load directlyrather than thru a relay, and the first and second heaters IIIG'and H6are energized from the line conductors I54 and I66 thru the first andsecondvoltage dropping or ballast resistors 184 and I82 respectively.The

first and second voltage dropping resistors I84 and I82 are providedmerely to simplify the construction of the heaters I06 and H6. Thecontrol could be built so as to energize the heaters I06 and H6 directlyfrom the line if the design of the heaters were changed.

The dotted lines show an alternative position for the stack switch inthe circuit and illustrates analternative way of energizing the secondheater IIB from the stack switch. In this case the closed cold stackswitch contacts are used instead of the closed hot contacts 92. Here thestack switch serves as a shunt for the heater rather than a seriesswitch in the heater circuit. When the stack switch elements are coldthe heater H6 is shunted and line voltage appears across the ballastresistor I 82. When the stack switch elements are heated so as to holdthe stack switch contacts 90 open, the heater H6 is energized in serieswith the ballast resistor I82 and part of the line voltage appearsacross each resistor. In this case the second ballast resistor I82 isessential. With this method of operation the second actuator isenergized and deenergized at exactly the same time in the control cycleas it would be if it were controlled by the closed hot contacts 92. Thefunctional-operopening of the safety switch and under predeterminedconditions for opening the safety switch, and a second motivating heaterfor the.

. second actuator, said second heater being enerationof the systemillustrated in Fig. 9 is identical with that of the system illustratedin Fig. 8.

An important feature of the invention concerns the method of energizingthe first and secand actuator heaters HIE and H6 by totally independentcircuits not in any way dependent upon the energization of the fuelburning means. This method of energizing the actuators of the safetyswitch obviates the need for series connection of the heaters I06 and H6in the motor circuit or in a motor control circuit, and is hereindistinguished from such prior control circuits by defining the heatercircuits of the present invention as being independent of the energiza-.

This inde-- tion of the fuel burning means pendent characteristic of thesafety switch actuators, in combination with the two-way acting safetyswitch affords a means for checking the action of the thermal device andadditionally checking the function of either heater without resorting toa series heater with all of its inherent incumbrances and non-universalapplication as pointed out in the introduction.

While a specific embodiment of the invention has been disclosed anddescribed, it will be apparent that many changes or modifications in thespecific details of the elements can be made without departing from thespirit of the invention,

and it istherefore desired that the invention be limited only by thescope of the appended claims.

What is claimed is:

1. A burner control system comprising means for burning fuel, a manuallyreset safety switch for controlling the fuel burning means, an automaticmeans for additionally controlling the fuel burning means, an actuatorfor the safety switch, a motivating heater for the actuator, said heaterbeing energized independently-of the energization of the fuel burningmeans by direct connection across a source of power by the automaticmeans, a second actuator for the safety switch responsive to combustionconditions, and a latch for the safety switch having two releasingpositions operated by the first and second actuators whereby relativemotion between the two actuators in either direction greater than apredetermined amount will open the safety switch.

2. A burner control system comprising means for burning fuel, a source'of power, a safety switch for controlling the fuel burning means, anautomatic means for additionally controlling the fuel burning means, anactuator for opening the safety switch, a motivating heater for theactuator; said heater being energized independently of the energizationof the fuel burning means by direct connection across a source of powerby the automatic means, a combustion responsive means; a second actuatorfor preventing the gized by direct connection across the source of powerby said combustion responsive means independently of the energization ofthe fuel burning means, whereby a check is provided upon theoperativeness of both of said heaters in each burner operation.

3. A burner control system comprising means for burning fuel, a safetyswitch for controlling the fuel burning means, a relay for additionallycontrolling the fuel burning means, an actuator for the safety switch, amotivating heater for the actuator,'said heater connected in parallelwith the relay, a second actuator for the safety switch operated afterthe establishment of combustion, and a latch for the safety switchhaving two releasing positions whereby a difference in action betweenthe first and second actuators in either direction greater than apredetermined amount will open the safety switc 4. A burner controlsystem comprising means for burning fuel, a manually reset safety switchfor controlling the fuel burning means, an actuator for the safetyswitch, a motivating heater for the actuator, said heater beingenergized in parallel with the fuel burning means, a second actuator forthe safety switch, a second motivating heater for the second actuator,said second heater being energized after the establishment ofcombustion, and a latch for the safety switch having two releasingpositions whereby a difference in action between the first and secondactuators in eitherdirection greater than a predetermined amount willopen the safety switch.

5. A burner control system comprising means for feeding fuel to aburner, means for energizing the fuel feeding means, a manually resetsafety switch for controlling the operation of the fuel feeding means,an actuator independently energized during the entire operation of thefuel feeding means for opening the safety switch after a predeterminedtime if combustion does not take place, and means responsivetocombustion conditions for opening the safety switch after combustiontakes place if said actuator is, not energized, said actuator andcombustion responsive means arranged to neutralize each other fornormally keeping the safety switch closed.

6. A burner control system comprising means for feeding fuel to aburner, means for energizing the fuel feeding means, a manually resetsafety switch for controlling the operation of the fuel feeding means, atime delay actuator for opening the safety switch and independentlyenergized during the entire operation of the fuel feeding means, and asecond time delay actuator for opening the safety switch energized uponthe establishment of combustion, said safety switch arranged to open ifeither actuator is energized alone but to remain closed if bothactuators are energized.

7. A burner control system comprising means for feeding fuel to theburner, a manually reset safety switch for controlling the operation ofthe fuel feeding means, a time delay actuator for pening the safetyswitch, automatic means for simultaneously and independently energizingthe fuel feeding means and the time delay actuator,

a second time delay actuator for opening the for energizing the safetyswitch, and combustion responsive means second actuator, said safety'fastened to the other actuator including a release member arrangetuators and to release sai tuators, a heater block and backwardreleasing positions fastened to one of said actuators switch arranged toremain closed it both actuators are energized.

8. A burner control system comprising means for burning fuel,a safetyswitch for controlling said system, a time delay actuator for the safetyswitch, a motivating heater for the actuator, a second actuator for thesafety switch responsive to combustion conditions, automatic means forcontrolling said fuel burning means and said heater, and means wherebysaid system is rendered inoperative by said safety switch after a timedelay in the event that either one of said actuators is ineffective.while the other is effective: F

9. A safety switch for a controller comprising a pair of actuators,latching means having two releasing positions fastened to one of saidactuators including a spring biased latch member, releasing meansfastened to the other actuator including a release member arranged toengage said latch member under certain conditions of operation by theactuatoraancl to release said latch member under different conditions ofoperation, and switching means held open by said latch member in itsreleased position.

10. A safety switch for a controller comprising a pair of U-shapedbimetal actuators, a heater for each of the actuators, said actuatorsarranged to compensate each other for temperatures other than thosecaused by the heaters, calibrating adjusting means associated with eachactuator, latching means having two releasing positions fastened to oneof said actuators including a spring biased latch member, releasingmeans d to engage said latch member under certain conditions ofoperation by the acd latch member under "different conditions ofoperation, switching means held open by said latch member in itsreleased position, and means for resetting the latch member and closingsaid switching means.

11. A burner control system comprising a fuel burning means, a switchfor controlling the fuel burning means, a pair of movable actuatorshaving hot and cold positions, one of said actuators being energizedconcurrently with the fuel burning means and being continually energizedduring the total time of energization of said fuel burning means,latching means operated by the actuators, said switch operated by saidlatching means, said latching means holding said switch closed when bothactuators are either in their hot or cold positions but opening saidswitch when one or'the other of the actuators is in its hot positionwhile the other is in its cold position.

12. A safety switch of the class described comprising a pair of bimetalactuators-of generally U-shaped configuration and thermally insulatedfrom each other, a heater for each of the acfor controlling the rate oftemperature rise of the actuators, latching means having forward I,releasing means'for said latch ing means'fastened to the other actuatorwhereby relative motion between the two actuators in either a forward orbackward direction of V over a predetermined amount releases saidlatch-- 7 ing means, said actuators arranged to-compen-.

sate each other for ambient temperature changes, and switching meansheld open bysaid latching means in-its released position.

13. A burner control apparatus comprising a for each of the heatersactress combustion responsive means, an actuating arm, a slip frictionmechanism for imparting motion of the combustion responsive means to theactuating arm, contacts opened and closed by the actuating arm, a safetyswitch, a first actuator for the safety switch, a heater for the firstac tuator controlled by external automatic means, a second actuator forthe safety switch, a heater for the second actuator controlled by saidcontacts, and latching means for said safety switch controlled by saidactuators, said latching-means being constructed and arranged so that adifference in action between said actuators in either direction greaterthan a predetermined amount will cause opening of the safety switch.

14. In a burner control apparatus, a base, a

pair of thermal actuators supported atone end from the base and havingtheir other ends free to move, an electric heater for each of thethermal actuators for actuating the same, a latch member actuated by themovable end of one of the thermal actuators, a release member having tworelease positions and actuated by the movable end of the other thermalactuator, biasing means for normally holding said latch member and saidrelease member in latching engagement, means for energizing one of theelectric heaters to release the latch member from the release member inone of its two releasing positions by the movement of the associatedtherelectric heater to release the release member in the other of itstwo release positions by movement of the associated thermal actuator,the

eifective to maintain the latch member in latching engagement with therelease member, and cooperating contact means operated upon release ofsaid latch member.

15. In a burner control apparatus, a burner, means for starting andstopping the burner, a base, a'pair of thermal actuators supported onone end of the base and having their other ends free tomove, an electricheater for each thermal actuator supported thereon for actuating thesame, one of said heaters energized during the entire operation of theburner, a latch member having first and second releasing positionssecured to the movable end of one of the thermal actuators, a, releasemember secured to the mov able end of the other thermal actuator, saidmembers having a latching engagement with each other, biasing meansnormally holding both said members in latching engagement, means forseparately'energizing the other electric heater, said releasing memberreleasing-the latch member in its first releasing position in case one Iof the heaters is energized alone for a time pemm and releasing thelatch member in its second releasing position in case the other heateris energized alone for a time period, but maintaining the memberslatched in case both heaters are energized within a time period afterthe burner starts or in case both heaters are deenergized within a timeperiod after the burner stops, said members arranged to prevent burneroperation in'their' unlatched position, and manp ual means forrelatching said members after they have been unlatched.

16. In a'burner control apparatus of the class described, a pair ofthermal actuators supported on one end and having their other endsarranged free to move in two directions, a latch member carried on thefree end of the first one of the 5 thermal actuators, a release membercarried on mal actuator, means for energizing the other energizing ofboth of said electric heaters being the free end of the second thermalactuator, means for normally biasing said members in latching engagementwith each other, an electric heater for each thermal actuator foroperating the same to move their free ends in the same direction,-thethermal actuators moving their free ends in the other direction whencooling, the independent movement of said first thermal actuator ineither direction releasing its latch member from engagement with therelease member, the independent movement of the second actuator ineither direction releasing the release described, a pair of thermalactuators supported at one end and arranged free to move their otherends in two directions, a latch member, a release member supported onthe movable end of one of the thermal actuators, a biasing springsupporting the latch member on the movable end of the other thermalactuator, said biasing spring normally holding said latch and saidrelease members in latching engagement, an electric heater for eachthermal actuator for operating the same tomove its free' end in onedirection, the thermal actuators moving their free ends in the oppositedirection when cooling, the latching engaging surfaces of the membersbeing of such an area as to require either thermal actuator to move ineither direction in accordance with a predetermined time interval tounlatch the members, the relative 7 movement of the first thermalactuator in either direction with respect to the second thermal actuatoreffecting an unlatching movement of the latch member from the releasemember, and the relative movement of the second thermal actuator ineither direction with respect to the first thermal actuator eifectingthe unlatching movement of the release member from the latch member, thecontemporaneous movement of both thermal actuators in the same directionmaintaining the latch and release members in engagement with each other,and a set of contacts actuated by the unlatching of the members.

18. A burner control system comprising a fuel burning means, a safetyswitch for controlling the fuel burning means, a pair of movableactuators for the safety switch, and latching means for the safetyswitch operated by the actuators and having two released positions, saidlatching means arranged to operate the safety switch only after therelative movement in either direction between the two actuators exceedsa predetermined amount.

19. A burner control system comprising fuel burning means, a safetyswitch for controlling the fuel burning means, a pair of movableactuators having hot and cold positions, one of said actuators energizedconcurrently with the fuel feeding means and the other actuatorenergized responsive to combustion conditions, latching means for thesafety switch operated by the actuators, said latching means holdingsaid safety switch closed when both actuators are in their hot or coldpositions but opening said safety switch when either of the actuators isin its hot position while the other is in its cold'position.

20. An oil burner system comprising means for burningfuel, a safetyswitch for controlling the fuel burning means, a pair of movableactuators for controlling the safety switch, latching means operated bysaid actuators for opening the safety switch when released, saidlatching means comprising members, one moved by each actuator and havingslidable engaging surfaces which cooperate with each other to remainengaged so long as both actuators move in unison in the same directionbut to disengage after relative motion between the actuators exceeds apredeermined amount in either direction.

21. A burner control system comprising a fuel burner, means for feedingfuel to the burner, a safety switch having open and closed positions forcontrolling the fuel feeding means, first time delay means for openingthe safety switch effective so long as the fuel feeding means isenergized, second means for opening the safety switch effective so longascfuel is being burned,

direction of movement releases said latching.

means, and switching means held open by said latching -means in eitherof its released positions.

23. A control system for a fuel burning means, the combination of, aswitch for controlling the fuel burning means, means including latchingmeans for causing said switch to remain in a predetermined position, afirst thermal actuator,

a second thermal, acuator, said first and second thermal actuators beingmechanically associated with and causing release of said latching meansupon a predetermined difference in action in either direction betweensaid thermal actuators, a heating means for the first thermal'actuator,and means for controlling said heating means and causing heating of saidsecond thermal actuator.

24. A burner control system comprising means for burning fuel, switchingmeans for controlling said fuel burning means, a first thermal actuator,

a second thermal actuator, mechanical means actuated in accordance withdifferences in action between said actuators and acting upon apredetermined difference in action in either direction between saidthermal actuators to actuate said switching means in a single electricalmanner, heating means for the first thermal actuator, and means forcontrolling said heating means and causing heating of said secondthermal actuator.

25. A controller of the class described comprising, a first thermalactuator, a first heating means for the first thermal actuator, a secondthermal actuator exposed to the same ambient temperature as the firstthermal actuator for compensating the controller for changes in ambienttemperature, a second heating means for the second thermal actuator, acontrol device, and mechanical means actuated by a predetermineddifference in action in either direction between said thermal actuatorsfor actuating said control device in a single manner.

26. A control system for a power consuming device, the combination of, aswitch for controlling the power consuming device,'means'includinglatching means for causing said switch to remain in a predeterminedposition, and means for releasing said latching means comprising a firstactuator and a second actuator, said actuators being mechanicallyassociated with and releasing said latching means upon a predetermineddifference in action thereof in one direction and also releasing saidlatching means upon a predetermined difference in action between theactuators in the opposite direction.

27. A control system for a fuel burner, .the combination of, a safetyswitch, a first thermal element, a second thermal element, meansactuated by a predetermined difference in action in either directionbetween said thermal elements for operating said safety switch, a powercircuit for saidburner and including said safety switch, a responsivedevice for openingand closing said power circuit for thereby startingand stopping the burner, first heating means for the first thermalelement, a second heating means for the second thermal element, saidheating means being connected in parallel with respect to each other andwith respect to said burner, bothofsaid heating means being controlledby the responsive device, and a combustion responsive switching meansinterposed in circuit with one only of said heating means, said lastmentioned switch closing upon presence of combustion.

28. In a control system for a burner, the combination of switching meansfor controlling the burner, a thermostatic element for actuating saidswitching means, electric heating means for said thermostatic elementand energized during the entire operation of the burner, a secondelement for controlling said switching means and having electricoperating means therefor, combustion responsive means for energizingsaid electric 013-- crating means upon presence of combustion, saidelements and switching means being arranged to prevent continuedoperation of the burner if either the electric heating means or theelectric operating means is energized alone, but to maintain the burnerin operation if both the electric heating means and the electricoperating means are energized.

29. In a control system for an electric motor driven fuel burner, thecombination of, a switch for controlling the burner, a firstthermostatic element for actuating said switch, said first thermostaticelement being arranged to open said switch upon movement of said firstthermostatic element in either direction, electric heating means forsaid first thermostatic element for causing movement of said firstthermostatic element in one direction, a second thermostatic element forcooperating with said first thermostatic element in controlling saidswitch, said second thermostatic element having electric heating meanstherefor and movable under the influence of the same, said secondthermostatic element in one position preventing movementof the switch toopen position due to movement of the first thermostatic element in saidone direction and in another position permitting movement of the switchto open position upon movement of the first thermostatic element in saidone direction, means including control means responsive to the demandfor heat from the burner for energizing r the electric heating means ofthe first thermo-= static element upon demand fonheat, and combustionresponsive switching means actuated upon presence of combustion forcontrolling the electric heating means of the second thermostaticelement ina manner preventing opening of the switch by movement of thefirst thermo static element in said one direction.

VIRGIL ROBINS TATE.

